Manufacture of alkyllead compounds



Patented Dec. 26, 1950 MANUFACTURE OF ALKYLLEAD COMPOUNDS George Calingaert and Hymin Shapiro, Detroit, Mich assignors to Ethyl Corporation, New York, N. Y a corporation of Delaware No Drawing. Application July 28, 1949, Serial No. 107,386

2 Claims.

This invention relates to a process for the manufacture of alkyllead compounds. More specifically it is directed to an improved process for the manufacture of tetraethyllead.

The present commercial process for manufacturing tetraethyllead proceeds by reacting a sodium-lead alloy, of composition controlled to correspond substantially to NaPb, with ethyl chloride. Under the best conditions obtainable in commercial operations only a limited amount of the lead present in the alloy is alkylated. Various other processes, employing alloys containing greater quantities or sodium than correspond to the composition NaPb heave been proposed in order to convert a greater proportion of the lead present in the alloy to alkyllead compounds. However, these methods are subject to the serious disadvantage that the ratio of sodium to lead for each of the alloy compositions must be maintained within extremely narrow limits, as otherwise the lead is inactivated and will not satisfactorily react with the alkylating agents. If the deviation from these narrow limits is great, the reaction with the alkylating agents practically ceases, for reasons not clearly understood. Thus the choice of a sodium-lead alloy is restricted to a few specific compositions.

It is an object of our invention to provide a new and improved process for the manufacture of lead alkyl compounds which overcomes the above objections. Another object of our invention is to produce substantial yields of tetraethyllead and related compounds by a process which can convert a large amount of the lead charged to the reaction into the desired end product.

We accomplish these objects by adding mag nesium to a sodium-lead alloy in a suiiicient quantity such that the resulting ternary alloy 'reacts readily with an alkylating agent, such as analkyl chloride.

We have found that to produce alkyllead compounds under conditions which are practical for commercial operation and from materials which are not prohibitive in cost, it is unnecessary to be restricted to the few sodium lead alloys of the prior art. On the contrary, we have made the surprising discovery that alkyllead compounds can be produced by the alkylation of sodium-magnesium-lead alloys having a wide range of sodium to lead ratios provided that the magnesium incorporated therein is present in an amount sufficient to permit alkylation of the lead without regard to the sodium-lead ratio. Both sodium and magnesium, in the alloys of our invention, react with the alkylating agent to form the corresponding sodium and magnesium salts. Therefore, the amount or" alkyllead compound produced from our alloys is dependent on the amount of both sodium and magnesium present. Thus, the proportion of lead converted to alkyllead compounds can be controlled within an unexpectedly broad range, by varying the proportions and amounts of the magnesium.

Although catalysts substantially improve the yield of alkyllead compounds obtainable in our invention they are not essential to our invention, since good yields can be obtained without the use of a catalyst. Furthermore, even though higher yields are obtainable with catalysts the use of catalysts may not be desirable. For example, the increased yield obtainable in the presence of a catalyst may be at the sacrifice of the product output capacity of the reaction equipment wherein volume limitations may be controlling.

We have discovered that ternary alloys con sisting of about 0.5 to 15 weight per cent sodium, about 3 to 19.5 weight per cent magnesium, and about to- Weight per cent lead are satisfactory in practicing the process of our invention. The amounts of sodium and magnesium, which can be referred to as secondary metals, can be varied independently within these prescribed limits so long as their sum remains within the limits of about 5 to 20 per cent by weight of the total alloy.

This invention is adaptable to the production of alkyllead compounds generally, such as tetraethyllead, tetramethyllead, dimethyldiethyllead, triethylphenyllead and tetrapropyllead. Nevertheless, for convenience specific reference hereinafter will be made to tetraethyllead, the most widely known alkyllead compound. Whenever in the following description this material is referred to, it is to be understood that other alkyllead compounds and mixtures thereof are also intended, in the same manner as though specifi cally referred to. Further, whenever in the following description reference is made to ethyl chloride as the ethylating agent, it is to be understood that other ethylating and alkylating agents can be substituted therefor or used in admixture therewith.

Generally, our invention is practiced as follows: the comminuted ternary alloy consisting of the magnesium-activated sodium-lead alloy is placed in a reaction vessel. The vessel is then closed except for the liquid feed line through which the fluid reactants are passed, and the necessary quantity of an alkylating agent such as ethyl chloride is then introduced into the autoclave. When it is desired to conduct our process in the presence of a catalyst, a catalyst such as diethyl ether is next introduced into the autoclave or the catalyst can be added along with the ethyl chloride.

In the working examples of our invention which follow, the yield of alkyllead compound will be based on the lead present in the ternary alloy employed, unless otherwise specified. Also, unless otherwise stated all parts and percentages herein are by weight. Further, ether means diethyl ether unless otherwise specified.

Example I A charge of 100 parts of sodium-magnesiumlead alloy consisting of 9.7 parts of sodium, 3.6 parts of magnesium and 86.7 parts of lead is added to the reaction vessel equipped with an agitator, a jacket for circulation of heating or cooling liquids, a reflux condenser, charging and discharging ports, liquid feed lines, and means for releasing the pressure. The alkylating agent. consisting of 110 parts of liquid ethyl chloride is added under pressure to the stirred alloy in the vessel over a period of one-half hour. By controlling the flow of liquid in the autoclave jacket and in the reflux condenser the temperatur of the reaction mass is permitted to rise from the initial temperature of 50 C. to a temperature of 85 C. during this f ed. The pressure in the autoclave during this period is allowed to rise to about 85 pounds per square inch gauge. The stirred reaction mass is maintained at a temperature of 85 C. and a pressure of 85 pounds for an additional one and one-half hours. This period is referred to as the cooking period. At the end of this period the pressure in the autoclave is reduced to atmospheric by venting for 15 minutes, while the temperature is maintained at 85 C. For an additional 15 minutes nitrogen is passed over the reaction mass while the autoclave is open to the atmosphere. With a stream of nitrogen passing through the reaction vessel the l ass is cooled to 45 C. over an additional 30 minute period. Thus a total reaction time of three hours is employed. The reaction mass is then charged from the reaction vessel and etc tilled or otherwise treated to recover lead product. The yield of product is 25. or a yield of 10.0 per cent based the weight of lead. Expressed in another way, yield is 44.6 per cent based on the comb sodium and magnesium present in the sodi magnesium-lead alloy.

Example II Using substantially the procedure descricer the foregoing example with the 1110i. ification that the cooking time is extended to two one-half hours at a maximum temperature of 70 C., parts of product is obtained from he alkylation of 100 parts of the sodium-magneszum-lead alloy consisting of 9.6 parts of sodium, 5.6 parts of magnesium and 84.8 parts of lead with parts of ethyl chloride. In this example the yield of product is 19.3 per cent.

Ezcample III Example I is repeated using 100 parts of the alloy consisting of 9.0 parts of sodium, 9.6 parts of magnesium and 81.4 parts of lead and 110 parts of ethyl chloride. With this modification the yield of alkllead product is 23.5 parts or 18.5 per cent.

Example IV Example II is repeated at a temperature of C. using 100 parts of the alloy consisting of 6.2 parts or sodium, 11.5 partsof magnesium and 82.3 parts of lead and 205 parts of ethyl chloride. The yield of product is 18.5 parts, or 14.4 per cent.

Example V Under the conditions of Example II 100 parts of the alloy consisting of 12.5 parts of sodium, 3.2 parts of magnesium and 84.3 parts of lead produces 22.0 parts of alkllead product, or a yield of 16.7 per cent.

Example VI Example II is repeated usin 100 parts of the alloy consisting of 5.5 parts of sodium, 3.0 parts of magnesium and 01.5 parts of lead and 23 parts of ethyl chloride. The yield of product is 5.7 parts, or 4.0 per cent.

Example VII Example II is repeated using 100 parts of the alloy consisting of 3.0 parts of sodium, 2.7 parts of magnesium and 94.3 parts of l ad and 235 parts of ethyl chloride. The yield of product is 7.7 parts, or 5.2 per cent.

Example VIII Example II is repeated using 100 parts of the alloy consisting of 6.0 parts of sodium, 7.0 parts of ma nesium and 87.0 parts of lead and 215 parts of ethyl chloride. lhe yield of product is 11.4 parts, or 8.4 per cent.

Example IX Example II is repeated at a temperature of 100 C. and with a reaction time of four hours using 100 parts of the alloy consisting of 0.5 part of sodium, 18.7 parts of magnesium and 80.8 parts of lead 200 parts of ethyl chloride. The yield of product is 6.7 parts, or 5.3 per cent.

Various alkylating agents can be employed in our process. For the most part, the alkylating agents of our invention are esters of inorganic acids which react with the sodium and magnesium present in the alloy and have the desired alkyl group, such as alkyl chlorides, alkyl bromides, alkyl iodides, alkyl phosphates and the like. In general, the inorganic acid ester alkylating agents are the mono-chloro, -b romo and -iodo derivatives of the parafiin hydrocarbons such as methane, ethane, propane, butane and pentane, the corresponding trialkyl phosphates, etc. For example, methyl bromide, methyl iodide, ethyl chloride, ethyl bromide, ethyl iodide, n-propyl chloride, n-butyl bromide, n-amyl chloride, n-amyl iodide, and triethyl phosphate can be successfully employed, alone or in admixture. Instead of or in admixture with the normal alkyl halides, their isomers may be used.

As examples of alkylating agents other than ethyl chloride which can be employed in the process of our invention, we employed the conditions of Example II with the alloy consisting of 9.6 parts of sodium, 5.6 parts of magnesium and 84.8 parts of lead and obtained yields of alkyllead compounds of 17.8, 18.5 and 12.6% when the alkylating agent consisted of ethyl iodide, ethyl bromide and propyl chloride respectively.

As mentioned previously, catalysts are not required for our invention. However, a catalyst may be used in order to increase the yield of alkyllead product. We have found that organic compounds containing an atom capable of chemical coordination with magnesium are particularly effective catalysts. Among these compounds are ethers, organo-ammonium derivatives, and amines. The amount of catalyst is not critical, and may be varied within wide limits, for instance, from 1 to 100 parts of catalyst to 100 parts of lead present in the alloy.

Examples of specific ethers which are effective for use in our process are diethyl ether, methylethyl ther, dipropyl ether, dibutyl ether, dihexyl ether, dimethyl ether of ethylene glycol, 1,4- dioxane and anisole. We prefer to use ethers as the catalyst and particularly the lower alkyl ethers, from methylethyl through dihexyl ether. Illustrative examples of organo-ammonium derivatives are tetraethylammonium iodide, trimethylethylammonium iodide and the like. Among the amines which may be used are triethylamine, trimethylamine and dimethylaniline. It is to be understood that combinations of the above and related catalysts can be employed with ood results.

While it is to be understood that good yields can be obtained from the process of our invention when employing ternary alloys of sodium, magnesium and lead with the alkylating agents as described herein in the absence of catalysts, with all of the alloys of our invention better results are obtained when employing catalysts. For example a yield of 14.1 per cent was obtained under the conditions of Example II when employing an alloy consisting of 9.0 parts of sodium, 9.6

parts of magnesium and 81.4 parts of lead in the absence of a catalyst, and a yield of 54.8 per cent was obtained when the reaction was conducted under the same conditions in the presence of 5 parts of diethyl ether.

For the best results, the alkylating agents of our process should be employed in excess of the amount required to react with all the sodium and magnesium in the alloy. If less than this amount of alkylating agent is used, the yield will be lower, but will still be good when determined on the basis of the amount of alkylating agent.

We prefer to introduce the alkylating agent as a liquid, and to conduct our alkylation reaction in the liquid phase. If ethyl chloride is the alkylating agent, the pressure within the autoclave is maintained within the range of about '70 to 125 pounds per square inch. In the same manner, the catalyst preferably is fed into the autoclave in the liquid phase under pressure. If desired the alkylating agent and catalyst can be mixed,

and the mixture introduced under pressure into the autoclave. In general, our process is completed within one-half to eight hours, but for most purposes we employ from 1 to 5 hours. While the temperature at which the process of our invention is carried out is not critical we prefer to employ temperatures within the range of about to about 100 C., although good results can be obtained at temperatures as high as 120 C.

In the practice of our invention it is advisable to follow the usual precautions in reactions of this type, and avoid the presence of excessive amounts of water.

It is evident from the numerous working examples described above that this invention may be varied within relatively wide ranges, both with respect to the reactants and the operating conditions, without departing from the scope thereof. From the instructions given, those skilled in the art will have no difliculty in selecting the best reactants and operating conditions for any desired purpose.

A many apparently widely different embodiments of this invention may be made without departing from the spirit and scope hereof, it is to be understood that we do not restrict ourselves except as defined in the following claims.

We claim:

1. A process for making lead alkyl compounds which comprises alkylating a sodium-magnesiumlead alloy in which the percentages by Weight are between about 0.5 and 15 sodium, between about 3 and 19.5 magnesium, and between about and lead.

2. A process for making tetraethyllead which comprises reacting an excess of ethyl chloride with a sodium-magnesium-lead alloy in which the percentages by weight are between about 0.5 and 15 sodium, between about 3 and 19.5 magnesium and between about 80 and 95 lead, said reaction being conducted at a temperature between about 60 C. and about C. for a time between about one and eight hours.

GEORGE CALINGAERT. HYlVlIN SHAPIRO.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,658,544 Youtz Feb. 7, 1928 1,661,809 Monroe Mar. 6, 1928 2,000,069 Dowing et a1. May 7, 1935 

1. A PROCESS FOR MAKING LEAD ALKYL COMPOUNDS WHICH COMPRISES ALKYLATING A SODIUM-MAGNESIUMLEAD ALLOY IN WHICH THE PERCENTAGES BY WEIGHT ARE BETWEEN ABOUT 0.5 AND 15 SODIUM, BETWEEN ABOUT 3 AND 19.5 MAGNESIUM, AND BETWEEN ABOUT 80 AND 95 LEAD. 